Apolipoprotein E (apoE) is a lipoprotein-associated glycoprotein synthesized in the CNS by glial cells, responsible for lipid transport within the brai. It has also been linked to a variety of CNS functions, including: neurodevelopment, inflammation, and synaptic plasticity. Importantly, APOE is the strongest genetic risk factor for the development of Alzheimer's disease (AD); it affects processes early in disease development and is known to influence normal brain function in the absence of AD pathology. There are three common human alleles: APOE-?2, APOE-?3, and APOE-?4. Compared to non-?4 carriers, a single copy of the ?4 allele confers an increased risk of 2- to 3-fold, while two ?4 alleles dramatically increase AD risk by 12-fold. At present, the mechanisms underlying apoE4-associated AD risk are unknown. My overarching hypothesis is that APOE genotype affects normal brain function before AD pathogenesis, specifically by affecting the development and network activity of organized neuronal populations in the brain. The objective of this research proposal is to investigate: 1) whether APOE genotype affects the functional development of neuronal networks in vitro; and 2) how apoE affects activity-induced network dynamics and excitatory neurotransmission. To test these objectives, I will first assess the formation and functional properties of neuronal networks in culture using multi-electrode arrays (MEA) (Aim 1). The MEA allows simultaneous measurement of electrical activity at 59 sites in a neuronal culture system. Cortical tissue will be harvested from APOE Targeted Replacement (TR) mice, a knock-in model expressing human APOE in place of murine APOE, and cultured onto MEAs for repeated electrophysiological recording as neuronal networks develop. This in vitro model allows me to test the contribution of each apoE isoform on neuronal networks, effectively reducing confounds present in other cell-based systems. I hypothesize that apoE4 may negatively impact the development of neuronal networks and cause overall decreased network activity compared to apoE2 or apoE3. Next, I will assess the influence of APOE genotype on activity-induced excitation and neuronal network dynamics using chemical Long-Term Potentiation (cLTP) (Aim 2). MEAs allow simple pharmacologic manipulation of apoE levels and signaling during cLTP to mechanistically determine the role apoE isoforms and its receptors play in activity-induced network dynamics. I hypothesize that apoE4 negatively affects cLTP-induced network dynamics. This interdisciplinary proposal represents a novel approach to understanding how APOE genotype contributes to large scale network formation and neuronal population activity. If my hypotheses are correct, then the information gained by these studies will be critical for the development of preventative therapeutics that compensate for apoE4-related brain changes.